The aim of this study is to investigate possible neuroendocrinological, neurotransmitter and membrane marker tests for depression. Depressed patients, free of psychotropic medication for at least 2 weeks, are tested over a 7-day period while on a low monoamine diet. Initially, two 24-hour urine collections are made for urinary MHPG and free cortisol estimations. Blood is drawn for platelet serotonin uptake and [3H]-imipramine binding assays, for plasma MHPG endorphins, norepinephrine and HVA assays. The cold pressor, thyrotropin-releasing hormone (TRH) and dexamethasone suppression (DST) tests are performed. A lumbar puncture is done to measure the neurotransmitter metabolites 5-HIAA, MHPG and HVA. The patients' symptoms are observer-recorded using the Hamilton Rating Scale, the PBRS and Bunney-Hamburg Scale as well as self-recorded using the POMS and Beck Scales. Premorbid personality is assesed on the Eysenck Personality Questionnaire (EPQ), the Fould's Hostility Questionnaire (HDHQ), sefl-esteem and obsessional-hysteroid questionnaires. Life events in the antecedent 6-month period are recorded using Paykel's method and premorbid marital and social support assessments are made. In the 8-month period from November, 1982 to June, 1983, we have investigated 46 depressed patients, including 25 recurrent affective disorder patients (17 melancholic in the current episode), 9 dysthymic disorder patients and 12 patients with a major depressive episode. Thus we will be able to examine these tests in 5 groups: recurrent affective disorder (endogenous depression), dysthymic disorder, "neurotic" depression, schizophrenia and normal volunteers. We will be able to examine both the sensitivity and specificity of these biological tests for depression.